AquaMost is developing a water treatment device based on a technology called photoelectrocatalytic oxidation (PECO). The focus for this project is using PECO systems to treat groundwater contaminated with organic pollutants released from leaking underground storage tanks. Two chemical classes are of particular concern: (1) aromatic hydrocarbons, particularly the BTEX chemicals benzene, ethyl benzene, toluene, and three isomers of xylene, and (2) fuel oxygenates, particularly methyl tert-butyl ether (MTBE). These chemicals are a significant risk to human health. Both chemical classes have acute and long-term toxic effects, and may be carcinogenic. For these reasons, considerable federal, state, and private resources are being expended to remove these chemicals from contaminated groundwater sites throughout the country. Several unique chemical characteristics of MTBE (e.g., high water solubility, high polarity, resistance to biodegradation) make it very difficult to remove from water using existing remediation technologies. The specific objectives of the Phase II project are to: (1) conduct long-term (> 6 months) field trials with commercial-scale PECO systems at several contaminated sites that differ with respect to contaminant levels, groundwater chemistry, etc. to obtain data on the long-term efficacy and performance of these systems, and (2) enhance the size and/or performance of the systems so that they can treat contaminated groundwater in a single pass at a flow rate of 5 to 10 gal/min (the current embodiment works at ~1 gal/min). Field tests will be performed at two primary sites and several secondary sites in conjunction with two environmental remediation companies that will serve as subcontractors on this project. These tests will help to answer several questions about the effectiveness of these PECO systems, including: (1) how will the technology perform under different field conditions? (2) What is the longevity and durability of the PECO unit electrodes under practical conditions? (3) How well does the technology enhance and complement current groundwater remediation technologies (e.g., activated carbon, air stripping, etc.)? (4) What are the operational and maintenance costs of using PECO to remediate contaminated groundwater? The PECO systems will be continually reengineered throughout these trials until an effective, robust, and economical commercial product is available for the market.